1. Field of the Invention
The present invention relates generally to satellite signal reception, and more particularly, to compensating for ionospheric delay in a multi constellation single Radio Frequency (RF) path Global Navigation Satellite Systems (GNSSs) receiver, hereinafter referred to as “a single frequency receiver.”
2. Description of the Related Art
Ionospheric interference is a common problem encountered in GNSSs. The ionosphere is a dispersive medium, which lies between seventy and one thousand kilometers above the Earth's surface, and effects a certain, frequency dependent propagation delay on signals transmitted from GNSS satellites. The ionosphere also affects GNSS signal tracking by a receiver. Notably, the ionospheric delay of a transmitted GNSS signal can cause an error of up to ten meters when calculating the exact geographic position on the Earth's surface of the receiver.
Delay from ionospheric interference can be almost completely corrected for by using multiple frequency observations, e.g., by transmitting and receiving signals at two different Global Positioning System (GPS) frequencies L1 and L2, from a single satellite. However, most GPS receivers do not receive both L1 and L2 frequencies.
Ionospheric delay cannot be eliminated in a conventional single frequency GNSS receiver, as a true Total Electron Count (TEC) value is very difficult to model and is highly sensitive to various parameters. Instead, these single (i.e., L1) frequency receivers often use ionospheric modeling, e.g., a Klobuchar Ionospheric Model or a NeQuick Ionospheric Model, to estimate and correct for transmission delay due to ionospheric interference.
Accordingly, a solution is needed for an apparatus and method for compensating for the ionospheric delay in a multi constellation, single frequency GNSS receiver, without the complexity or cost associated with dual frequency receivers and ionospheric modeling.